1. Field of the Invention
The present invention relates to a fuel controller of an internal combustion engine, more particularly, to a fuel controller which corrects time-aged characteristic variation of air-flow sensor like hot-wire air-flow sensor used for controlling flow of fuel.
2. Description of the Prior Art
Physical characteristic of hot-wire air-flow sensor is subject to variation by adverse influence of materials adhered to the surface of hot-wire and as a result, error occurs in the volume of fuel which is fed to the internal combustion engine. This results in the occurrence of more pollutant in exhaust gas and degraded driving performance. Characteristic of vane-type air-flow sensor is also variable by materials deposited on sliding members, and thus, above problems also occur. In addition, variation of physical characteristic variation caused by deposited material is largely dependent on the volume of fuel passing through the air-flow sensor. Conventionally, negative feedback control by applying air-fuel (A/F) ratio sensor is effective for correcting characteristic of those sensors mentioned above. To correct physical characteristic of sensors in specific regions where the negative feedback control is inapplicable, Japanese Patent Application Laid-Open No. 58-150057 (1983) discloses a system for implementing study correction. This is substantially a device for correcting air-fuel ratio by negatively feeding back signals from A/F ratio sensor installed to the exhaust tube of the engine, where memory of the device memorizes the negative feedback volume so that the device can correct the basic value of fuel control operation according to the content of memory even in such a region where the negative feedback control is inapplicable.
When implementing the study correction by estimating physical characteristic variation of the air-flow sensor from the correction volume in the region in which characteristic variation of air-flow sensor can be corrected by negative feedback means in a specific region under presence of much volume of flowing fuel where specific air-fuel ratio thicker than the theoretical A/F ratio is required and the negative feedback control cannot be executed, if there are transitory error air-fuel ratio which peculiarly affects the above specific region when executing negative feedback correction, then the studied correction value to be estimated becomes incorrect and aggravates erroneous air-fuel ratio in the region where large volume of fuel flows. As a transitory influential error mentioned above, there is such an error of the air-fuel ratio which normally occurs when purging evaporated fuel caught by canister through the air intake passage of the engine. Purging of evaporated fuel generates substantial influence when the engine is driven under low load, i.e., when less volume of air is sucked. Influence of purge remains substantially low when much volume of air flows. Consequently, unless the influence of purge is eliminated, estimated study correction cannot be achieved.